In preparing fish paste products such as boiled fish paste (or kamaboko), it has been commonly practiced to shape raw fish meat paste with use of an extruder.
The extruder of this sort has been hitherto so constructed that, as illustrated in FIG. 3, a hopper 12 into which a food material is thrown is set on a pedestal 11 and the food material thrown into the hopper 12 is press-forwarded to an extruder main body 15 through a transport pipe 14 by the action of a material-feeding pump 13. Then the food material is extruded into a given shape from a nozzle 16 of the extruder main body 15, and so cut as to have a given length by means of a cutter (not shown) or the like.
However, products obtained by shaping a simple food material with use of the above extruder have been monotonous in their food texture and appearance, being unsatisfactorily a little poor in ideas. Thus, it is recently practiced to form the nozzle into a multiple pipe structure or the like so that a plurality of food materials different in the material and color can be simultaneously extruded.
As an attempt therefor, Japanese Patent Publication No. 38189/1981 or Japanese Patent Publication No. 29067/1983 propose an apparatus in which a cylindrical nozzle is formed into a multiple pipe structure (e.g., an outer-and-inner double-wall pipe structure) to form a circular (or ring-like, when viewed from the front) discharge end along its periphery, which circular discharge end is further partitioned so as to form arcs (when viewed from the front), and outer-layer materials different in colors are respectively extruded from the arclike discharge ends while the nozzle is rotated, so that a pattern can be applied to the surface in a spiral form.
The above apparatus makes it possible to apply to the surface a unique pattern composed of spiral stripes, but have had the problems that the structure of the apparatus is complicated, resulting in a high production cost and also making it difficult to perform the maintenance such as internal cleaning.